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Thurston County Lakes

Blue-Green Algae Blooms

Blue-Green Algae(Our thanks to the Pierce County Environmental Health Department for granting permission to use portions of its Web site for this page.)

red arrowAlso see state Department of Health brochure on Blue-Green Algae Blooms (PDF)

Introduction

When you visit local lakes in Thurston County, you might notice a bright green color or thick scum along the shore. This might make you hesitant to take a dip -- and it should! The green color is caused by algae, a primitive plant form that occurs in lakes and streams. Given the right conditions of sunlight, temperature, and nutrients, algae populations can multiply dramatically, often causing a "bloom."

Many lakes in Thurston County are nutrient-rich, or "eutrophic," and experience algae blooms every summer or fall. Algae blooms are a natural occurrence in these nutrient-rich lakes. 

Algae come in different shapes, colors and types, some more noticeable than others. Blue-green algae (Cyanophyta), have the nasty possibility of producing toxins (poisons). 

What Is A Blue-Green Algae Bloom?

Blue-green algae reproduce rapidly in fresh water when the amount of sunlight, temperature and nutrients are adequate. Within a few days a "clear" lake, pond or ditch can become cloudy with algae growth. This is called a bloom. Blue-green blooms usually float to the surface and can be several inches thick near the shoreline.

A blue-green algae bloom:

  • Is usually very noticeable by the pea-green or turquoise-green color of the water. It is often mistaken as a paint spill.
  • Is made up of extremely small organisms that are hard to pick up or hold.
  • Can be bright green, or bluish, brownish or reddish green.
  • Is most common in the summer and fall but can occur anytime.

Although blue-green blooms can create nuisance conditions and undesirable water quality, most blue-green blooms are not toxic.

What is a Toxic Bloom?

Some blue-green algae produce toxins or poisons. Eventually the toxins break down and are destroyed naturally. Ingesting the algae while they are still poisonous can cause serious illness. In their toxic form, blue-green algae can kill pets, waterfowl, and other animals. Residential drinking water taken from a lake may be affected.

Signs of a toxic bloom may include:

  • Large numbers of dead fish, waterfowl or other animals.
  • Sudden, unexplained sickness or death of a cat or dog, especially if it has algae on its mouth, legs or feet.
  • A skin rash on humans after being in the water.

How Can I Tell Whether a Bloom is Toxic?

Whether a particular bloom is actually toxic cannot be determined without special testing. Moreover, testing only provides information on that single sample, at a particular moment of time. Even the scientific experts have not yet solved the mystery of why, when, and how algae turns toxic. In other words, there is no way to predict when, or if, an algae bloom will be toxic. If the water at your beach looks bad, don't swim in it. If you really want to swim, you should find another beach that is clear.

What If I See a Bloom?

When an algae bloom is occurring in a lake, please take these simple precautions:

  • If the water at a lake looks bad, don't swim in it. Find another place to swim. 
  • If you do enter the water, towel dry and shower. Blue-green algae can cause a skin rash in some people with sensitive skin. And remember: there is often the possibility of swimmer's itch, which is a parasite common in our lakes. 
  • Keep children and pets away from the water. Poisoning is more severe the smaller the person or animal, and the larger the amount of toxin ingested. Children can become ill after accidentally swallowing algae in water. Pets, too, can become sick after drinking the water or licking algae-covered paws.

Health Tips

  • Get proper medical or veterinary attention right away if you, your children, pets, or livestock have signs of poisoning.
  • Blue-green algae can produce nerve toxins and liver toxins. Signs of neurotoxin poisoning usually appear within 15-20 minutes after ingestion. In animals, signs include weakness, staggering, difficulty in breathing, convulsions and death. In people, signs may include numbness of the lips, tingling in fingers and toes, and dizziness. Algae can also cause skin rashes.
  • It may be hours or days before signs of liver poisoning appear. Liver toxins can cause abdominal pain, diarrhea and vomiting in humans, and death in animals.

How You Can Help Prevent Blue-Green Algae Blooms

Algae blooms are likely to occur during sunny, calm weather when high concentrations of nutrients are present in the water. People can have a big effect on the amount of nutrients in a lake. Two important nutrients algae require are phosphorous and nitrogen. These are found in animal and human waste (sewage) and in fertilizers. Excessive amounts of nitrogen and phosphorus may lead to "nutrient loading" and eventually to an algae bloom. To help decrease nutrient loading:

  • Maintain or restore native plants around lake shorelines and streams that feed the lake. Native wetland plants help filter water and don't require pesticides or fertilizers for maintenance.
  • Be extremely cautious with lawn and plant fertilizers and pesticides. Don't over-water, over-fertilize, or use more than the recommended amount of pesticides.
  • Malfunctioning or damaged septic systems can be a major cause of nutrient loading into nearby water. Proper care and maintenance of your septic system are essential. Have your system pumped and inspected every three to four years.
  • Prevent surface water runoff from agricultural and livestock areas. Do not allow livestock to drink or defecate in streams or lakes. Don't feed waterfowl.
  • Take steps to prevent erosion around construction and logging operations. Erosion can carry nutrient-rich soil into nearby lakes.

How to Report a Blue-Green Algae Bloom

To report a blue-green algae bloom, call Sue Davis at Thurston County Environmental Health, 867-2500 or e-mail daviss@co.thurston.wa.us.

 

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